This invention relates to a process and apparatus for electrophotographic reproduction utilizing a virtual image of an electrostatic charge on a conductive support and transferring this image to a dielectric support followed by developing and fixing the image so as to make the same visible and permanent. More particularly, this invention relates to an improved process wherein defects and background imperfections resulting from the separation of the dielectric support and the photoconductive support are reduced or eliminated.
Although the general process for producing electrophotographic images by forming an electrostatic charge on a conductive support coated with a photoconductive layer followed by transferring of this image onto a dielectric layer with subsequent developing and fixing of the image is well known, these processes present serious difficulties since there is an undesirable discharge when the two supports are separated subsequent to the transfer of the charge image. As noted above, the electrophotographic process involves the bringing of a dielectric support and a photoconductive support into close or into virtual contact, either statically or dynamically, so that the transfer of charges can occur under the influence of an electric field. when these two supports are separated, prior to fixing and developing the image transferred to the dielectric support, discharges occur which cause the appearance of configurations known as Lichtenberg figures which are also developed during developing, causing a disagreeable and irreglar background on the copy sheet. This phenomenon is believed to be caused by the photoconductive surface carrying a residual charge which has not been completely discharged subsequent to transfer so that it remains partially dielectric, thereby causing a separation between what is in reality two dielectric surfaces.
Prior art attempts to remove this difficiency in the basic process by the short-circuiting of the two supports prior to separation or establishing at separation a field opposite that utilized for effecting the transfer have only given partial relief to the problem of dielectric discharge creating undesirable backgrounds.